A heat-resistant molded body, which is obtained by causing a binder to adhere to a glass fiber or the like, and by molding the resultant into a mat shape, has been widely used as, for example, a heat-insulating material for a house, a warehouse, an apparatus, an instrument, or the like. A phenol-formaldehyde binder has been widely used as the binder. However, the phenol-formaldehyde binder involves a problem in that unreacted formaldehyde remains in a molded body, and hence formaldehyde is discharged after the construction of a house or the like. Accordingly, a binder that does not discharge formaldehyde has been investigated.
In, for example, Patent Literature 1, there is a disclosure of a binder for a mineral fiber, which is formed of a vinyl copolymer (A) having an organic acid (salt) group (a) and a hydroxyl group, and having a weight-average molecular weight of from 500 to 100,000. In Patent Literature 1, there is a disclosure that the binder for a mineral fiber exhibits the following effects: (1) the binder is free of formaldehyde, and formaldehyde is not discharged from a heat-insulating material obtained by bonding mineral fibers to each other with the binder and molding the resultant into a mat shape; (2) the binder is superior to a conventional phenol resin in adhesive property with a mineral fiber and in restorability of the heat-insulating material against compression; (3) a binder in the form of an aqueous solution or an aqueous dispersion out of the binders of the present invention is excellent in environmental adaptability and is easily recycled; and (4) the binder shows satisfactory physical properties, such as an adhesive property, even in a neutral region.
In Patent Literature 2, there is a disclosure of a glass fiber binder, which is formed of an aqueous solution of: (1) a copolymer formed of a product of a reaction between a polymerizable carboxylic acid or an anhydride thereof, or a mixture thereof, and a hydroxyalkyl acrylate or methacrylate having a C2 to C8 alkyl group, or a mixture thereof; and (2) an alkali metal salt of a phosphorus-containing acid. In Patent Literature 2, there is a disclosure that the binder has low viscosity when the binder is not cured, and has structural rigidity when the binder is cured.
In Patent Literature 3, there is a disclosure of an aqueous binder for a mineral fiber containing a (co)polymer (A) having at least two carboxyl groups or acid anhydride groups, a compound (B) having at least one hydroxyl group and at least one amino group, and water, in which the neutralization ratio of carboxyl groups derived from the carboxyl groups or the acid anhydride groups in the (A) is from 36 eq % to 70 eq %, and the neutralization is neutralization with an amino group in the (B). In Patent Literature 3, there is a disclosure that the aqueous binder for a mineral fiber exhibits the following effects: (1) the binder is free of formaldehyde; (2) the binder is excellent in water resistance and hydrolysis resistance; (3) the binder is excellent in adhesive property with a mineral fiber; and (4) a mineral fiber laminate obtained by bonding mineral fibers to each other with the binder is excellent in restorability against compression.
In Patent Literature 4, there is a disclosure of an aqueous binder for an inorganic fiber containing an acrylic resin having an acid value of from 350 mgKOH/g to 850 mgKOH/g, a cross-linking agent containing at least one kind of dialkanolamine, a curing accelerator, and an ammonium salt of an inorganic acid, in which: the molar ratio of the total number of moles of hydroxyl groups and imino groups in the cross-linking agent to the number of moles of carboxyl groups in the acrylic resin is from 0.8 to 1.5; and the pH of the binder is adjusted to from 6.0 to 8.0 with a volatile basic compound. In Patent Literature 4, there is a disclosure of the following. An ammonium ion is volatilized as ammonia by the heating of the ammonium salt of the inorganic acid in a binder-curing step, and hence the residue remains as an acid in the binder. Accordingly, the neutralization of an alkali component eluted from an inorganic fiber can suppress the hydrolysis of a cross-linked portion in the binder, and hence enables long-term maintenance of various physical properties of an inorganic fiber heat-insulating sound-absorbing material.
In Patent Literature 5, there is a disclosure of an aqueous binder for an inorganic fiber heat-insulating sound-absorbing material containing an acrylic resin having an acid value of from 350 mgKOH/g to 850 mgKOH/g, a cross-linking agent containing at least one kind of alkanolamine, and an ammonium salt of an inorganic acid, in which: the binder contains 5.5 parts by mass to 10 parts by mass of the ammonium salt of the inorganic acid with respect to 100 parts by mass of the total of the acrylic resin and the cross-linking agent; the molar ratio of the total number of moles of hydroxyl groups, amino groups, and imino groups in the cross-linking agent to the number of moles of carboxyl groups in the acrylic resin is from 0.8 to 1.5; and the pH of the binder is adjusted to from 5.0 to 8.0 with a basic compound. In Patent Literature 5, there is a disclosure of the following. The aqueous binder for an inorganic fiber heat-insulating sound-absorbing material is a binder formed of the acrylic resin and free of formaldehyde, and hence the binder cures without emitting formaldehyde and the environmental load of its exhaust gas or the like can be reduced. In addition, the binder is excellent in curability, and hence even when a heat curing temperature is low, the cross-linking reaction of the binder rapidly progresses to provide a strong binder cured product.
As described above, various binders for glass fibers and the like each free of formaldehyde have been proposed. However, each of those binders involves a problem in that the strength of a glass fiber or the like treated with the binder is not sufficient, or a problem in that the storage stability of the binder is not sufficient.